In the past line narrowing modules for gas discharge laser systems of the type mentioned above have included a tuning optical element, e.g., a tuning mirror, e.g., an RMax mirror, which is applicants' assignee's designation for a tuning mirror having maximum reflectivity for the wavelength of the laser system, e.g., nominally 248 nm for a KrF laser system and 193 for an ArF laser system It will be understood by those skilled in the art that the “maximum reflectivity” applies generally the same across a relatively broad band of several hundred picometers (“pm”) at which the laser system lases before being line narrowed in the line narrowing module, e.g., to about 0.12 pm full width half maximum (“FWHM”) and about 0.3 pm for the integral of energy in the spectrum amounting to 95% of all energy about some center wavelength of the spectrum at about the peak, i.e., commonly referred to as E95% or simply E95.
Applicants assignee has proposed certain improvements to such laser systems currently available laser systems sold by applicants' assignee, e.g., in single chambered models, e.g., ELS 7XXX models and in dual chambered systems, e.g., master oscillator-power amplifier (“MOPA” systems, e.g., XLA-1XX and XLA-2XX systems available from applicants' assignee. These improvements are aimed at making bandwidth control and bandwidth stability more robust. The present application relates to aspects of embodiments of such improvements, e.g., to the above referenced application Ser. No. 11/000,684.